Q+A-How bad is insecurity in Nigeria's oil heartland?

June 18 (Reuters) - Nigerian militants have carried out a series of attacks against oil facilities in the Niger Delta since the army launched its biggest offensive in the region for years last month.

Here are some questions and answers about the security situation in the Niger Delta, home to Africa's biggest oil and gas industry and one of the world's largest wetlands.

IS THE SECURITY SITUATION IMPROVING OR DETERIORATING?

The main militant group, the Movement for the Emancipation of the Niger Delta (MEND), has launched what it calls "Hurricane Piper Alpha" since the military offensive, warning it will attack oil facilities across the region.

But the attacks so far appear to have been carried out by only one faction -- supporters of Government Tompolo, who was targeted by the military campaign. Apart from an attack on Royal Dutch Shell (RDSa.L: Quote, Profile, Research) in Bayelsa state on Wednesday, they have so far been largely focused in Delta state further west.

Industry and security sources say it is virtually impossible to fully protect hundreds of kilometres of pipeline running through remote swamplands from guerrilla-style attacks and expect such strikes to continue.

But MEND has so far shown itself unable to repeat the sort of spectacular raids it launched after it first burst onto the scene in late 2005, knocking out more than a quarter of Nigeria's oil output in a matter of weeks.